How can I detect the frame from video streaming that contains a graffiti on city wall?
ResNet is an architecture for object recognition and you may use it to do your classification task.  Fast RCNN may improve your results but is a more difficult architecture to implement.  If you want to go in this direction the best place to start is the arxiv paper of the Fast R-CNN (arxiv.org/abs/1504.08083).  If I am not wrong, there is an implementation of fast-rcnn in pytorch if you really want that.

You seem to be new to deep learning.  I would strongly recommend starting simple. ResNet-50 will probably be more than enough for your application. Moreover, I suggest using a lib like fast.ai.